Comparison between pyranometers and encapsulated solar cells as reference PV sensors-outdoor measurements in real conditions

Three types of reference sensors for outdoor measurements and PV (photovoltaic) installation, monitoring purposes have been analyzed: pyranometers, reference solar cells, and equivalent technology solar cells (ETSCs). All of the set points measured with an automatic data acquisition system during a sunny day on tilted and fixed platforms and analyzed by statistical linear regression passing to the (0.0) point allow the determination of the calibration values of reference sensors. The calibration deviation value obtained for ETSC using a pyranometer as a reference sensor was ±2%, and a value of ±0.5% was obtained when the reference sensor was another ETSC. With this method, spectral mismatch and temperature corrections and special ground preparation are not necessary for the conditions in Madrid. The same analysis is helpful for rejecting nonlinearity and badly encapsulated sensors. It is concluded that a single solar cell with the same technology, encapsulation system, frame, and box connection as the PV modules with a precision resistor is the best reference sensor for outdoor PV measurements